Patent attributes
After forming a field insulating film 12 on a substrate, sacrificing or gate oxidation films are formed as oxidation films 14a and 14b. An ion implantation layer 18 is formed by one or plurality of implantation process of argon (or fluoride) ion in an element hole 12a using a resist layer 16 as a mask via the oxidation film 14a. When the oxidation films 14a and 14b are used as sacrificing oxidation films, gate oxidation films are formed in the element holes 12a and 12b after removing the resist film 16 and the oxidation films 14a and 14b. When the oxidation films 14a and 14b are used as gate oxidation films, the oxidation films are once thinned by etching and then thickened after removing the resist layer 16. The gate oxidation film 14a is thicker than the gate oxidation film 14b by forming the ion implantation layer 18.
